1. Field of the Invention
The present invention relates to communication to and from structures and, more particularly, to systems and methods for monitoring and communication to and from structures.
2. Description of Related Art
As our military aircraft fleet ages, Applicants recognize that it will become increasing important to provide prognostic health management (PHM) of a structure such as a frame of an aircraft or other type of vehicle. For example, PHM may provide a way to predict when the aircraft structure has degraded to the point where it no longer meets safety margins due to metal fatigue. In newer aircraft made from composite materials, structural monitoring will also be required to help predict the sudden catastrophic failure of the composite, which can happen when material defects rapidly propagate in the structure. Wiring, for example, can further degrade the integrity of the structure, especially for composites, and can increase the cost of retrofitting a sensor network such as in an aircraft fleet. Today, wireless sensor network solutions are typically based on radio frequency (RF) or infrared light, but these approaches can increase the detectability of military aircraft to an enemy. In addition, RF solutions can be high power, requiring relatively large battery sources for the embedded sensors. Wireless communication via RF can produce unwanted RF signatures and interference in some applications as well. RF communication may also be impractical in some applications due to excessive multipath or RF interference.
It has been known to use ultrasound communication for in situ monitoring of an injection molding process, for example, but there is a need for in situ sensors that provide real-time measurements of material stress to provide PHM of various structures such as aircraft or other vehicles.